Summary While preparing the vessel for departure, the main engine was pre-lubricated, blown through and started in the astern mode. As the engine fired, an explosion occurred in the upper section of the exhaust system. There was resulting damage to the economizer lower hopper and the main engine exhaust pipe rain-cap and a cloud of soot was ejected from the stack top. The exhaust pipe rain-cap landed on the upper deck of the vessel. The engine controls were immediately moved to the stop position following the explosion. There were no injuries, nor was there any pollution. Minor damage occurred to the vessel's main engine exhaust system and extensive damage occurred to the rain cap. Ce rapport est galement disponible en franais. Other Factual Information Particulars of the Vessel The Mitsubishi-Sulzer RTA84 fitted to the CAPECHARLES is a two stroke, uniflow-scavenged, crosshead-type diesel engine with a bore of 840mm and a stroke of 2400mm. The engine uses 380 cst (centistoke) fuel at sea and during manoeuvring. The cylinder liner lubricating oil, called Texaco TARO Special cylinder lubricant, is supplied to cylinder lubricating quills. The lubricating quills are arranged around the upper part of each cylinder from a cylinder-lubricating pump driven by oil from the main bearing oil system. Under emergency running conditions, oil from the cross-head bearing oil system may be used to drive the cylinder lubricating pump by opening and adjusting a valve which by-passes the flow-regulating valve. In this case, either the engine operation or oil flow to the pump may have to be regulated to ensure correct cylinder liner lubrication. The by-pass valve was reportedly found to be leaking slightly during post-explosion examination of the engine by the vessel's engineers. It was also reported that the cylinder lubrication storage tank contained about 230 litres less than it should have when checked after the explosion. Exhaust gas from each cylinder flows into the exhaust manifold from where it enters the turbochargers. Upon exiting the turbochargers, the exhaust gas flows into the starboard side of the economizer lower hopper. This hopper is a fabricated, open-topped metal box, approximately 3890mm high, which is 5371mm long at the top and 4081mm long on the bottom, and is 2620mm wide on the top and 2284mm wide on the bottom. The side and bottom plating is 4.5mm thick. A drain is fitted in the bottom plating. The exhaust gas enters the exhaust gas heat exchanger and travels upwards for a distance of 8440mm, passing across the tube banks. The top of the exhaust gas heat exchanger is covered with a shaped transition piece 825mm high leading into the circular exhaust pipe. From the top of the exhaust gas heat exchanger the exhaust gas passes directly upwards through the exhaust pipe to vent via the rain hood at the stack top. While underway, steam generated using the exhaust gas heat exchanger is utilized to supply domestic heating needs, heat the heavy fuel oil and drive a turbo alternator set. In port, an oil-fired boiler is used to supply domestic and fuel heating needs. Electrical power is supplied by diesel generator sets. During a follow-up visit to the vessel, while it was loading and discharging containers, the temperature in the economizer was noted to vary between 154C in the lower section and 109C in the upper section. On 30 December 1996, while preparing to depart the Ceres Container terminal for sea, the main engine was pre-lubricated and blown through. There were no reports of any liquid exiting the indicator cocks while blowing through. The main engine was started in the astern mode from the Bridge control station. Very shortly after the engine was started, a sharp, loud, noise was heard by those on the bridge wing. This noise was followed by a crash as the exhaust pipe rain hood landed on the upper deck of the accommodation block amid a cloud of soot and dust. Post occurrence examination of the exhaust system revealed the following items. No damage was reported to the exhaust trunking attached to the main engine, nor to the turbo chargers. No damage to the exhaust gas piping between the turbochargers and the lower economizer hopper was reported. Some damage to the exterior of the lower economizer hopper was reported. A noticeable bulging of the forward and after sides of the hopper was evident, and also a general displacement of the sheet metal covered insulation panels. A bulging of the hopper plating on the forward, after and starboard faces on the inlet side above the exhaust gas inlet level was reported. On the interior, tears in the hopper bottom, up to 300 mm in length at some locations where the internal stiffeners join the side plating, were reported. Various other tears in the plating and a slight bending of the internal angle bar stiffeners on the sides and bottom were also reported. The interior was evenly coated with soot and showed no signs of flame impingement. No visible damage to the exhaust gas heat exchanger pipes was reported. A slight displacement of some of the sheet metal insulation panels on the sides of the heat exchanger was found throughout its height. There was a slight distortion of the heat exchanger plating generally. An internal examination of the tubes of the exhaust gas heat exchanger was conducted after the inspection covers had been removed. The examination reportedly revealed that at approximately 2/3 height the tubes were clean of all the light soot that had been noted elsewhere. The soot blowers showed no damage and, when tested in the presence of the class surveyor, operated normally. Severe damage occurred to the exhaust rain-hood as a result of being ejected from the stack top and landing on the upper deck. The exhaust rain-hood has a mass of approximately 800kg. During the time alongside while loading and discharging, routine planned maintenance is carried out by the engine-room crew. Examination of the main-engine injectors, carried out after the explosion, reportedly revealed no abnormalities. The ship staff alleged that the origin of the explosion was in the exhaust trunk before the turbo-chargers due to the ignition of accumulated cylinder-liner lubrication oil. In a case involving a similar-sized vessel, where an economizer fire occurred, it was noted that the engine manufacturer had stated in a service letter that oil-wetted soot may ignite at temperatures as low as 150C. Action Taken To prevent a re-occurrence, Univan Ship Management Ltd. has issued instructions to all its vessels fitted with Sulzer RLA, RLB and RTA series of engines that the by-pass valve is to be fitted with a locking device and that the integrity of the valve is to be inspected from time to time to detect possible leakages.